Can competition experiments be used to evaluate the potential efficacy of new water hyacinth biological control agents?

摘要

Two factors are of concern when considering a new biological control agent for introduction. The first is the safety of the organism (i.e. its host specificity) and the second is the potential for the organism to control the target weed (i.e. its efficacy). Methods for evaluating safety before introduction are well known but scant attention has been paid to pre-release evaluation of the efficacy of the candidate organisms. This is understandable inasmuch as the agent's performance depends on the presence or absence of density-dependent population regulating factors that will differ between the donor area and the recipient country. However, this is of less concern when the agent has already been introduced elsewhere, where it can be studied without the influence of density-dependent regulators. Experiments comparing the effectiveness of the new agent with that of another, more widely known agent, can then be used to determine the relative value of the-former with the known impacts of the latter. Additive series analysis (inverse linear models) of competition between water hyacinth and water lettuce as mediated by herbivory has been suggested as a means of judging the relative value of new agents. This approach is fraught with difficulties inasmuch as there will always be unknown factors that affect the abundance of new agents (i.e. biotic resistance), but it could enable assessment of the potential value of the proposed introduction and, in so doing, perhaps pre-empt the introduction of risky agents that provide little control value.